Method and apparatus for reducing the signalling bandwidth load by reporting measurements in differential manner in a multicast message

ABSTRACT

A signalling method for reducing the bandwidth needed for communicating measurement values from at least a first source base station ( 11, 12, 13, 14 ) to at least a 5 first target base station ( 21, 22, 23, 24, 25 ) connected through a core base station ( 10 ) comprising the steps of—reporting at least a first measurement value from the at least first source base station ( 11, 12, 13, 14 ) to the core base station ( 10 ), —preferably sorting the measurement values in descending order,  10 —including, in the core base station ( 10 ) value information about the at least first measurement value in a multicast message, —transmitting the multicast message to the at least first target base station ( 21, 22, 23, 24, 25 ), characterized in that the value information is determined as a first difference between a maximum value and the first measurement value.

TECHNICAL FIELD

The present invention relates in general to communication in a cellularnetwork and more specifically to the reporting of measurements in such anetwork.

BACKGROUND AND RELATED ART

In an OFDMA/SC-FDMA based system the available bandwidth is sub-dividedinto several resource blocks or units as defined, for example in 3GPP TR25.814: “Physical Layer Aspects for Evolved UTRA”. According to thisdocument a resource block is defined in both time and frequency. In thedownlink each user terminal estimates the downlink channel quality oneach resource block and reports the measured quality to the network. Thedownlink channel quality can be indicated by various types ofmeasurements carried out by the terminal, such as channel qualityindicator (CQI), received signal strength indicator (RSSI), transmitpower of the terminal, signal to interference and noise ratio (SINR)etc.

In the uplink on the other hand, the base station, often referred to asNode B, can carry out various types of measurements such as downlinktotal transmit carrier power, downlink transmit carrier power perresource block, uplink received total wide band power, resource blockusage etc. Based on the measurements reported by the terminal and themeasurements performed by the base station, the network can dynamicallyallocate or schedule the resource blocks to the users for datatransmission. The network also utilizes these measurements to performother types of radio resource management tasks such as handover,congestion control, admission control etc.

In CDMA systems each user is allocated the entire bandwidth butdifferent users are distinguished by assigning a separate orthogonaland/or scrambling code. However in OFDMA/SC-FDMA systems, each cellpossesses several resource blocks depending upon the system bandwidth.This is because the bandwidth of a resource block is much smaller thanthat of the system bandwidth. In an E-UTRA, according to the currentworking assumption, the resource block comprises of 180 kHz in frequencyand 0.5 ms in time. As an example there will be 48 and 96 resourceblocks for 10 MHz and 20 MHz respectively since some portion of thebandwidth acts as guard band and is therefore left unused. Some radioresource management functions such as scheduling, inter-cellinterference coordination, congestion control etc would require theterminal and the base station to carry out various kinds of measurementson each or on a group of resource blocks. Furthermore, in order to trackfast temporal channel variations the measurements are to be reportedquite frequently, such as every transmission time interval (TTI), whichis 1 ms. This would involve considerable signalling overheads leading tocapacity loss.

In E-UTRA, different types of measurements from a base station may bereported to several neighbouring base stations. This would lead toduplication of measurement reports over mesh type network such as inE-UTRA, where all the base stations are logically connected to eachother. This would imply considerable signalling overheads over theinterfaces between the base stations. It has therefore been proposed tomulticast measurements to a group or a set of base stations that hasjoined the distribution list. This implies that measurements fromdifferent base stations shall be multicast to several set of basestations.

International Patent Application No PCT/SE2005/001579 discloses a methodfor reducing the signalling load especially on the radio interface inE-UTRA by reporting measurements in differential manner, that is,reporting each measurement value as a difference between the measurementvalue and a maximum value defined for the relevant type of measurement.This differential method is also described in 3GPP TR 25.814: “PhysicalLayer Aspects for Evolved UTRA”.

The state of the art solution reduces the signalling overheads for eachmeasurement individually. However in the current system a terminal mayhave to report several different kinds of measurements. Similarly eachbase station may report several types to measurements to itsneighbouring base stations. This means there will still be considerableoverhead due to measurement reporting.

OBJECT OF THE INVENTION

It is an object of the invention to reduce the signalling load in awireless communication network, and in particular the signalling loadbetween base stations.

SUMMARY OF THE INVENTION

This object is achieved according to the present invention by a basestation for use as a core base station in a tree structure comprising atleast a first and a second branch of base stations, said base stationcomprising receiving means for receiving from at least a first sourcebase station information about at least a first measurement valueintended for at least a first target base station, generating means forgenerating a multicast message including information about the at leastfirst measurement value, and transmitting means for transmitting themulticast message, said base station being characterized in that thegenerating means comprises calculating means for calculating adifferential value based on the at least first measurement value and atleast a maximum value for the at least first measurement value.

This object is also achieved by a base station arranged to communicatein a cellular network with at least one other base station, through acore base station, said base station comprising receiving means forreceiving from the core base station a multicast message related to atleast one measurement value from a source base station, and retrievingmeans for retrieving at least one measurement value intended for it,said base station being characterized in that the retrieving meanscomprises extracting means arranged to extract a value information whichis a differential value based on the measurement value and at least amaximum value for the measurement value and a calculating means arrangedto calculate the measurement value based on at least the differentialvalue and the maximum value.

Hence, according to the invention a base station that can act as a corebase station and a base station that can act as a target base station,respectively, are achieved. According to the invention, one or more ofthe source base stations will present their measurement values to thecore base station, which will calculate differential measurement valueswhich requires less bandwidth than the actual values. The differentialmeasurement values are then included in a multicast message andtransmitted to the target base station. The target base station, in turnis able to interpret the multicast message, extract the informationintended for it and calculate the actual measurement value on the basisof the differential value.

The object is also achieved by a signalling method for communicatingmeasurement values from at least a first source base station to at leasta first target base station connected through a core base stationcomprising the steps of

-   -   reporting at least a first measurement value from the at least        first source base station to the core base station,    -   including, in the core base station value information about the        at least first measurement value in a multicast message and    -   transmitting the multicast message to the at least first target        base station, said method being characterized in that the value        information is determined as a first difference between a        maximum value and the first measurement value.

This method is chiefly performed in the core base station, for creatingthe differential measurement values and multicast messages as discussedabove.

The object is also achieved by a signalling method for retrievingmeasurement values from at least a first source base station in at leasta first target base station, said source and target base stations beingconnected through a core base station comprising the steps of

-   -   receiving in a first target base station a multicast message        from the core base station;    -   determining, on the basis of the multicast message, at least a        first measurement value intended for the first target base        station;        said method being characterized in that the step of determining        the measurement value comprises the steps of extracting value        information related to the measurement value from the multicast        message and calculating the measurement value based on the value        information an at least a maximum value for the measurement        value.

This method is performed in the target base station for retrieving theactual measurement value intended for it.

The differential measurement reporting according to the inventionenables more efficient use of existing IP multicasting in the transportnetwork. According to the invention the signalling overhead is reducedand unnecessary measurement reports are prevented.

It should be noted that the source and target base stations do not haveto be physically connected through the core base station as long asthere is a logical connection through the core base station.

In the core base station, the calculating means is preferably arrangedto determine value information related to a second measurement value asa second difference between the first difference and the secondmeasurement value and to include this value information in the multicastmessage. The corresponding method preferably comprises the additionalsteps of determining value information related to a second measurementvalue as a second difference between the first difference and the secondmeasurement value and including this value information in the multicastmessage.

In a particularly advantageous embodiment the core base station furthercomprises ordering means arranged to select the highest measurementvalue of a number of reported measurement values as the firstmeasurement value and then handling the measurement values in descendingorder. The corresponding method also comprises the step of selecting thehighest measurement value as the first measurement value and thenhandling the measurement values in descending order. This will minimizethe size of the differential values, thereby minimizing the bandwidthrequired to transmit them.

The generating means is preferably arranged to include in the multicastmessage, for each measurement value, information about the source basestation, the target base station and the type of measurement. In thisway each target base station will be able to tell which values areintended for it and how the actual measurement value can be retrieved.

The method performed in the core base station may be used for differenttypes of communication that are particularly advantageous:

-   -   For communicating several measurement values, each belonging to        a different measurement type from one source base station to one        target base station.    -   For communicating several measurements related to several        different source base stations to one or more target base        stations.    -   For communicating several measurements, each belonging to a        different measurement type related to one source base station to        several target base stations.

The target base station preferably further comprises determining meansfor determining whether the multicast message comprises valueinformation intended for at least one other target base station andcomprising forwarding means for forwarding the multicast message to atleast one further base station if this is the case. The correspondingmethod comprises the steps of determining whether the multicast messagecomprises value information intended for at least one other target basestation and, if so, forwarding the multicast message to the at least oneother target base station.

The target base station also preferably comprises calculating meansarranged to prune the multicast message before forwarding it to the atleast one other target base station. In this way the multicast messagewill only contain information needed by subsequent base stations,thereby further reducing the bandwidth required.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail in the following, by wayof example and with reference to the appended drawings in which:

FIG. 1 shows a cellular network.

FIG. 2 illustrates transmission of measurement reports between basestations in a cellular network.

FIG. 3 shows a connection scheme for a number of base stations.

FIG. 4 is a flow chart of the procedure for creating and transmittingthe multicast message according to the invention

FIG. 5 is a flow chart of the procedure for receiving the multicastmessage according to the invention.

FIGS. 6 and 7 are examples of multicast messages according to theinvention.

FIG. 8 illustrates in more detail a core base station and a target basestation.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 shows a cellular network in which a number of base stations 1 areinterconnected. All the base stations are served by the same accessgateway 3. It should be noted that FIG. 1 is a logical diagram in thesense that the direct connections between any two base stations shown inthe Figure may be implemented in reality through one or more other basestations.

In the current E-UTRA architecture each base station 1 is connected toall other base stations under the same access gateway (AGW) 3 forming alogical mesh network as shown in FIG. 1. As shown in FIG. 1 each basestation can report its measurement to the neighbour base stations via anX2 interface or the so called Node B-Node B interface. Although thisinterface is only shown between some of the base stations it should beunderstood that it is present between all base stations connected to thesame access gateway. Each base station 1 shall be able to report certaintype of measurements to at least its closest neighbour base stations.The purpose of these measurements is to indicate the load or occupancyof radio resources at the base station. Some measurements may alsodepict the usage of transport network resources on the interfacesbetween the base stations and between the base stations and the accessgateway. This allows the base station to carry out multicell radioresource management, i.e. a base station takes into account the loadsituation at the neighbouring base stations when allocating resources,doing handover, admitting new user etc. Obviously in such a distributedarchitecture there would be considerable signalling overheads on X2interfaces.

FIG. 2 illustrates the inventive multi-cellular differential reporting,which is realized in IP based multicasting or broadcasting networks. TheE-UTRA transport network shall be based on IP technology. A number ofsource base stations S1, S2, S3, S4, that is, base stations which, inthis example are reporting measurements, each transmit to one or more ofa number of target base stations T1, T2, T3, T4, T5, T6. In the exampleshown in FIG. 2, for example, source base station S1 transmits to targetbase stations T1, T3 and T5. Source base station S2 transmits to targetbase stations T1 and T6.

According to a preferred embodiment of the invention each multicastsource reports the difference between different base stationmeasurements of the same type that are destined to base stationsbelonging to the same tree branch or multicast route, as will bediscussed in more detail below.

FIG. 3 shows a connection scheme for a number of base stations arrangedin what is known as a core-base tree, in which a first base station 10is connected to a first and a second branch of base stations. The firstbranch comprises base stations 11, 12, 13, 14, 15, where 11 is branchedto 12 and 13, and 13 is branched to 14 and 15.

The second branch comprises base stations 21, 22, 23, 24, 25, where 21is branched to 22 and 23 and 23 is branched to 24 and 25. Of course thisis intended as an example only. The base stations may be physicallyinterconnected in any possible way. The base stations include routerfunctionality.

The first base station, or core base station, 10, to which both branchesare connected, is arranged to control communication between all otherbase stations, including base stations arranged in the same branch.Therefore, the first base station has more information about the otherbase stations, including look-up tables with routing information etc.

In this mechanism multicast messages, which comprise measurements inthis case, are first sent to the core. The core base station as well aseach router keeps track of the distribution lists (i.e. the list oftarget base stations intended to receive measurement reports). Asmentioned above, in this context, a router is typically implemented aspart of the base station. The application of the different reportingmechanism in core base tree routing would require the core to first sortall the measurements of the same kind from different base stations anddestined to the same tree branch or route, in decreasing order ofmagnitude and multicast them as their relative difference.

As an example, consider a situation in which base station 11 wishes totransmit information about a measurement value to base station 24. Basestation 12 wishes to transmit information about a measurement value tobase station 25. Similarly, base stations 13 and 14 both wish totransmit to base station 21. Each of the transmitting base stations 11,12, 13 and 14 transmits its information to the first, or core, basestation 10. The measurement values do not have to be related to the sametype of parameter, as long as they are reported on the same scale orusing the same unit, such as dB or percent. The first base station 10recognizes that the measurement values are intended for base stations inthe same, second, branch and are reported on the same scale. In thiscase the first base station 10 may include all the measurement values ina multicast message for the second branch.

The procedure for creating the multicast message according to theinvention is shown in FIG. 4. This procedure is performed in the corebase station 10 after receiving at least one measurement value from atleast one source base station intended for transmission to at least onetarget base station.

In step S41 the measurement values received from the source basestations are arranged in descending order. This is an optional step,which will minimize the values to be included in the multicast message,thus minimizing the size of the multicast message.

In step S42 the first base station subtracts the greatest measurementvalue from the maximum value.

In step S43 the core base station includes the result of the subtractionperformed in step S42 in the multicast message. To enable retrieval ofthe information in the target base station the following informationmust be included: the transmitting base station, the receiving basestation, the measurement type and the result of the subtraction.

In step S44 it is determined whether more values should be included tothe multicast message. If yes, go to step S45; if no, go to step S47.

In step S45, the first base station subtracts the next greatestmeasurement value from the preceding greatest measurement value.

In step S46 the first base station includes the result of thesubtraction performed in step S45 in the multicast message. Thisincludes information about the transmitting base station, the receivingbase station, the measurement type and the result of the subtraction.The procedure then returns to step S44.

When it is determined in step S44 that there are no more measurementvalues, the multicast message is transmitted to the second branch, instep S47.

FIG. 5 is a flow chart of the procedure when a message is received inthe second branch.

In step S51 the receiving base station receives the multicast message.The first time this is performed this will be the first base station 21in the second branch.

In step S52 the receiving base station extracts the differential valueand, if necessary, all preceding differential values.

In step S53, the receiving base station determines the measurement valueon the basis of the subtractions performed in the procedure of FIG. 4.

In step S54 it is determined if the message should be forwarded to oneor more other base stations in the second branch. This is the case ifthere are more values in the multicast message. If yes, go to step S54;if no, end of procedure.

In step S55 the message is pruned. This involves deleting the valueextracted by the receiving base station and, of course, thecorresponding identifiers. This may cause the need to recalculatesubsequent differential values in the multicast message. Pruning is notnecessary but will reduce further the signalling load in the network, atthe expense of some increased processing requirements in each of thetarget base stations.

In step S56, the receiving base station forwards the pruned message tothe next base station. For base station 21 this means forwarding themessage to base station 22, which then becomes the receiving basestation.

Of course, in step S52, if a there is no differential value intended forthe receiving base station it will just pass the message on to the nextbase station in the tree, which then becomes the receiving base station.If no measurement value is intended for subsequent base stations in abranch, the message does not have to be forwarded to this branch. Forexample, if the message contains no value intended for base station 24or 25, then base station 23 does not have to forward the message at all.

Assuming that the measurement value reported by base stations 12, 11, 13and 14 are 70%, 85%, 50% and 90%, respectively, the multicast messagewill look as in FIG. 6. Assuming that all these values are above thethreshold for reporting values, they will all be included in themulticast message, as shown in FIG. 6. If one or more of the values arebelow the threshold they will not be included, and the message will beshorter. The measurement values will be included in the following order,referring to the source base station: 14, 11, 12 and 13, as stated in afirst field 61 of FIG. 6. Hence, the target base stations will be 21,25, 24 and 21, in this order, as listed in a second field 62. A thirdfield 63 states, for each value, the type of measurement it refers to.The measurement values to be reported will be 100−90=10, 90−85=5,85−70=15 and 70−50=20, as reflected in a fourth field 64.

Table 1 shows a distribution list related to the example shown in FIG. 6which has one column for each source base station 11, 12, 13, 14 and onerow for each target base station 21, 22, 23, 24 and 25. The letter Y(for yes) or N (for no) indicates that a measurement value from therespective source base station should, or should not, respectively, bereported to the respective target base station.

TABLE 1 11 12 13 14 21 N Y N Y 22 N N N N 23 N N N N 24 N N Y N 25 Y N NN

FIG. 7 shows a general multicast message according to the invention. Ina first field 71 the source base stations are listed in the correctorder, preferably in such a way that the first source base station, thatis, the one reporting the highest value is listed first and the onereporting the lowest value is listed last. To make it more general, thesource base stations are denoted S₁, S₂ etc. and the target basestations are denoted T₁, T₂, etc. in FIG. 7. In a second field 72 thetarget base stations are listed in the corresponding order, so that thetarget base station that is to receive the value from the firstmentioned source base station is listed first, etc. The type ofmeasurement value is listed in the corresponding order in a third field73 and in a fourth field 74 the differential values are listed.

In the fourth field 74 the first differential value is the result of thesubtraction of the first measurement value M₁ reported from the firstsource base station from the maximum value M_(max) defined for themeasurement value scale. The second differential value is the result ofthe subtraction of the second measurement value M₂ from the firstmeasurement value M₁. The following differential values are calculatedas M_(i)−M_(i-1), i=3, 4 . . . As stated above the source base stationsare preferably ordered in such a way that M₁ is the highest measurementvalue, M₂ is the second highest, etc.

A particularly advantageous situation occurs if one or more of themeasurement values are equal. This is the case, for example if the samebase station reports the same measurement value to all base stations ofa branch. In this case one or more of the differential values will bezero, thus requiring a minimum of bandwidth. In case all these targetbase stations belong to a certain group identified by a common groupidentity, then only one measurement value, which is the differencebetween the maximum vale (M_(max)) and the measurement quality needs tobe reported, requiring even lower bandwidth (or number of bits).

Another special case will be if several source base stations arereporting measurement values to the same target base station.

The inventive idea can also be used for reporting several measurementvalues of different measurement types between one source entity and onetarget entity. Each of the source and target entity, respectively, inthis case may be a mobile terminal or a base station. According to theinvention the measurement values are reported in terms of differences.This is referred to as multifarious differential reporting.

For this method to be effective, the measurement values must be reportedon the same scale. Examples of values that are suitable for differentialreporting in this context are mean total transmitted carrier power, meantransmitted carrier power per channel (or per resource block), meantransmitted carrier power per antenna branch, received total power,total resource block usage etc.

For differential multifarious reporting, let M different measurementtypes, expressed on the same scale (e.g. percentage or on dB) with thesame maximum and minimum values, Ω_(max) and Ω_(min), respectively, andsorted in decreasing order of magnitude as follows:

[λ₁, λ₂, . . . , λ_(M)] and whose corresponding ID are [θ₁, θ₂, . . . ,θ_(M)]

The measurement reporting entity (user terminal or base station) reportsdifferential measurements {λ} and ID {θ} to the target entities (e.g.base stations) as follows:

[μ₁, μ₂, . . . , μ_(N)], where: ∥1=Ω_(max)−λ₁; μ₂=λ₂−λ₁ μ_(N)=λ_(N−λ)_(N−1)

As before measurements, which are above a certain threshold (Ω_(min)))could be reported to further reduce the overheads.

Several measurements are reportable or are expected to be reported onthe same scale, such as percentage. Examples of such base stationmeasurements are: total transmitted carrier power, transmitted carrierpower per branch, transmitted carrier power per resource block, downlinktotal resource block usage, uplink total resource block usage, downlinkresource block activity, uplink resource block usage, link packet lossrate over X2 interface etc.

However, all measurements may not always be expressed on the same scale.In that case measurements that are reportable on same scale can bere-grouped and sent group wise in a differential way, e.g. percentagegroup, dB group, dBm group etc. It should be noted that this reportingmechanism is highly suited for base station measurement reports, i.e.exchange of measurements between base stations in transport network. Butthe idea is applicable and easily realizable also for reports from userterminals.

FIG. 8 illustrates in more detail the core base station 10 and one ofthe target base stations 21 of FIG. 3. The core base station 10comprises receiving means 101 for receiving measurement values from thesource base stations (not shown). From the receiving means themeasurement values are forwarded to a generating means 103 comprising acalculating means 105 for calculating differential values based on themeasurement values as described above. The generating means 103preferably also comprises an ordering means 107 for ordering themeasurement values in descending order before calculating thedifferential values. The generating means 103 generates a multicastmessage including the differential values and possibly other informationas discussed in connection with FIGS. 6 and 7. The multicast message isforwarded through a transmitting means 109 to the target base station21.

The target base station 21 comprises receiving means 210 for receivingthe multicast message and retrieving means 212 for retrieving themeasurement value intended for it. To this end the retrieving means 212comprises extracting means 214 and calculating means 216. The extractingmeans 214 is arranged to extract a value information which is adifferential value included in the multicast message by the core basestation 10 and the calculating means 216 is arranged to calculate theactual measurement value based on the extracted differential value. Thetarget base station 21 also comprises transmitting means 218 forforwarding the multicast message to one or more other base stations ifit is determined by a determining means 219 that this should be done.Preferably the target base station 21 also comprises a pruning means 220between the determining means and the forwarding means 118, for pruningthe message before it is forwarded. Pruning involves removing from themulticast message any values that are not needed by any subsequenttarget base station, and is discussed in more detail above.

As will be understood, the units shown in FIG. 8 are not usuallyseparate physical units but may be implemented as parts of a computerprogram, or as different program modules, running on the same ordifferent processors in the respective base station. The division intounits is arbitrary and intended as an example only, to illustrate thedifferent functions performed by the base stations.

1. A base station for use as a core base station in a tree structurehaving at least a first branch and a second branch of base stations, thebase station comprising: means for receiving, from at least a firstsource base station, information about at least a first measurementvalue intended for at least a first target base station; means forgenerating a multicast message including information about the at leastfirst measurement value, wherein the generating means comprises meansfor calculating a first differential value based on the at least firstmeasurement value and at least a maximum value for the at least firstmeasurement value; and means for transmitting the multicast message. 2.The base station of claim 1, wherein the calculating means is arrangedto determine second value information related to a second measurementvalue as a second difference between the first differential value andthe second measurement value and to include the second value informationin the multicast message.
 3. The base station of claim 2, furthercomprising ordering means for selecting a highest measurement value of anumber of reported measurement values as the first measurement value andthen handling the measurement values in descending order.
 4. The basestation of claim 2, wherein the generating means is arranged to includein the multicast message, for each measurement value, information aboutthe source base station, the target base station, and a type ofmeasurement.
 5. A base station arranged to communicate through a corebase station in a cellular network with at least one other base station,the base station comprising: means for receiving, from the core basestation, a multicast message related to at least one measurement valuefrom a source base station; and means for retrieving at least onemeasurement value intended for the base station, wherein the retrievingmeans comprises means for extracting a value information that is adifferential value based on the measurement value and at least a maximumvalue for the measurement value, and means for calculating themeasurement value based on at least the differential value and themaximum value.
 6. The base station of claim 5, further comprising meansfor determining whether the multicast message includes value informationrelating to at least one other target base station, and means forforwarding the multicast message to at least one other target basestation based on a determination by the determining means.
 7. The basestation of claim 6, further comprising means for pruning the multicastmessage before forwarding the multicast message to the at least oneother target base station.
 8. A signaling method for communicatingmeasurement values from at least a first source base station to at leasta first target base station connected through a core base station,comprising: reporting at least a first measurement value from the firstsource base station to the core base station; including, by the corebase station, value information about the at least first measurementvalue in a multicast message, wherein the value information isdetermined as a first difference between a maximum value and the firstmeasurement value; and transmitting the multicast message to the atleast first target base station.
 9. The method of claim 8, furthercomprising determining second value information related to a secondmeasurement value as a second difference between the first differenceand the second measurement value, and including the second valueinformation in the multicast message.
 10. The method of claim 9, furthercomprising selecting a highest measurement value as the firstmeasurement value and then handling the measurement values in descendingorder.
 11. The method of claim 9, further comprising including in themulticast message, for each measurement value, information about thesource base station, the target base station, and a type of measurement.12. The method of claim 8, wherein several measurement values, eachbelonging to a different measurement type, are communicated from onesource base station to one target base station.
 13. The method of claim8, wherein several measurements related to several different source basestations are communicated to one or more target base stations.
 14. Themethod of claim 8, wherein several measurements, each belonging to adifferent measurement type related to one source base station, arecommunicated to several target base stations.
 15. A signaling method forretrieving measurement values from at least a first source base stationin at least a first target base station, the source and target basestations being connected through a core base station, comprising:receiving, in a first target base station, a multicast message from thecore base station; and determining, on the basis of the multicastmessage, at least a first measurement value intended for the firsttarget base station, wherein determining the measurement value comprisesextracting value information related to the measurement value from themulticast message, the value information including a first differentialvalue based on the at least first measurement value and at least amaximum value for the at least first measurement value, and calculatingthe measurement value based on the value information and the at leastmaximum value for the measurement value.
 16. The method of claim 15,further comprising determining whether the multicast message comprisesvalue information intended for at least one other target base station,and if so, forwarding the multicast message to the at least one othertarget base station.
 17. The method of claim 16, further comprisingpruning the multicast message before forwarding the multicast message tothe at least one other target base station.